<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Behavior in Threaded Programs</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 9.1.2 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="libpq - C Library"
HREF="libpq.html"><LINK
REL="PREVIOUS"
TITLE="SSL Support"
HREF="libpq-ssl.html"><LINK
REL="NEXT"
TITLE="Building libpq Programs"
HREF="libpq-build.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2011-12-01T22:07:59"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
><A
HREF="index.html"
>PostgreSQL 9.1.2 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="SSL Support"
HREF="libpq-ssl.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="libpq.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 31. <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> - C Library</TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="Building libpq Programs"
HREF="libpq-build.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-THREADING"
>31.18. Behavior in Threaded Programs</A
></H1
><P
>   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> is reentrant and thread-safe by default.
   You might need to use special compiler command-line
   options when you compile your application code.  Refer to your
   system's documentation for information about how to build
   thread-enabled applications, or look in
   <TT
CLASS="FILENAME"
>src/Makefile.global</TT
> for <TT
CLASS="LITERAL"
>PTHREAD_CFLAGS</TT
>
   and <TT
CLASS="LITERAL"
>PTHREAD_LIBS</TT
>.  This function allows the querying of
   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>'s thread-safe status:
  </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><A
NAME="LIBPQ-PQISTHREADSAFE"
></A
><CODE
CLASS="FUNCTION"
>PQisthreadsafe</CODE
>
     </DT
><DD
><P
>      Returns the thread safety status of the
      <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> library.
</P><PRE
CLASS="SYNOPSIS"
>int PQisthreadsafe();</PRE
><P>
     </P
><P
>      Returns 1 if the <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> is thread-safe
      and 0 if it is not.
     </P
></DD
></DL
></DIV
><P
>   One thread restriction is that no two threads attempt to manipulate
   the same <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object at the same time. In particular,
   you cannot issue concurrent commands from different threads through
   the same connection object. (If you need to run concurrent commands,
   use multiple connections.)
  </P
><P
>   <TT
CLASS="STRUCTNAME"
>PGresult</TT
> objects are read-only after creation, and so
   can be passed around freely between threads.
  </P
><P
>   The deprecated functions <CODE
CLASS="FUNCTION"
>PQrequestCancel</CODE
> and
   <CODE
CLASS="FUNCTION"
>PQoidStatus</CODE
> are not thread-safe and should not be
   used in multithread programs.  <CODE
CLASS="FUNCTION"
>PQrequestCancel</CODE
>
   can be replaced by <CODE
CLASS="FUNCTION"
>PQcancel</CODE
>.
   <CODE
CLASS="FUNCTION"
>PQoidStatus</CODE
> can be replaced by
   <CODE
CLASS="FUNCTION"
>PQoidValue</CODE
>.
  </P
><P
>   If you are using Kerberos inside your application (in addition to inside
   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>), you will need to do locking around
   Kerberos calls because Kerberos functions are not thread-safe.  See
   function <CODE
CLASS="FUNCTION"
>PQregisterThreadLock</CODE
> in the
   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> source code for a way to do cooperative
   locking between <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> and your application.
  </P
><P
>   If you experience problems with threaded applications, run the program
   in <TT
CLASS="FILENAME"
>src/tools/thread</TT
> to see if your platform has
   thread-unsafe functions.  This program is run by
   <TT
CLASS="FILENAME"
>configure</TT
>, but for binary distributions your
   library might not match the library used to build the binaries.
  </P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="libpq-ssl.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="libpq-build.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>SSL Support</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="libpq.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Building <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> Programs</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>